Laser induced spectroscopy is utilized to detect minute amounts of trace elements in material samples. For example, U.S. Pat. No. 5,379,103 issued to Zigler on Jan. 3, 1995, the contents of which are incorporated herein by reference, discloses a method and apparatus for in situ detection of minute amounts of trace elements, wherein a laser energy pulse from a laser source is focused on the surface of an analysis sample by a focusing lens or other optical means to vaporize a portion of the sample and thereby generate a plasma. Spectral changes emitted by the plasma are analyzed with a spectrometer to identify trace elements within the analysis sample.
It has been proposed to utilize trace element detectors of the type described above to directly monitor various material streams, such as powders and slurried mixtures of solids and waters, during normal processing operations, as opposed to taking a discrete sample of the material stream to a laboratory site for analysis. Direct monitoring provides many advantages over discrete sampling, including the ability to adjust the process being monitored in real time based on the results of the analysis. It has been found, however, that the inherently dusty and dirty conditions associated with direct monitoring of material streams in certain applications, for example in mining and ore refining operations, requires frequent cleaning of the focusing lense of the trace element detector. In addition, the vaporization of the material sample stream during the detection and analysis process creates miniature shock waves that result in small amounts of the sample material being scattered onto the focusing lens of the trace element detector. As a result, the overall efficiency of the direct monitoring process suffers due to the necessity of frequently cleaning the focusing lens of the trace element detector.
In view of the above, it is an object of the invention to provide a mechanism that permits direct monitoring of a material stream with a trace element detector while overcoming the problems associated with the buildup of debris on the focusing lens, thereby allowing highly efficient operation of the trace element detector.